This application is a continuation of international patent application no. PCT/EP00/07619, filed Aug. 5, 2000, designating the United States of America, the entire disclosure of which is hereby incorporated herein by reference. Priority is claimed based on Federal Republic of Germany application no. 199 40 610.3, filed Aug. 27, 1999.
This invention relates to an air filter for an internal combustion engine including an air filter housing which encloses a filter space and has a housing wall, an air inlet,.and an air outlet. The invention further relates to a method of producing such an air filter.
It is generally known that all vehicles are subject to regulations regarding maximum permissible noise emission. The automobile manufacturers are therefore obliged to build low-noise vehicles as far as possible. Due to the low noise emission of the vehicle and the high sound insulation of the passenger compartment, the driver typically receives information on the operating state of the engine only through the speedometer. Many drivers perceive this as a drawback.
Federal republic of Germany published patent application no. DE 197 04 376 A1discloses an air filter arrangement with an conduit having an acoustic effective leading from the air filter to the passenger compartment. This conduit is intended to transmit sound into the passenger compartment and to inform the driver of the operating state of the engine. The conduit is sealed in an airtight manner by a membrane, which vibrates during operation and transmits these vibrations into the passenger compartment. The drawback of this solution is the use of an additional component, which must be extended through the engine compartment all the way to the passenger compartment or driver""s compartment. The installation space required for this purpose is available only to a limited extent in the complex construction of today""s vehicles and furthermore this structural assembly results in an increase in weight.
It is an object of the invention to provide means for influencing the intake noise of an internal combustion engine of a motor vehicle.
Another object of the invention is to provide an intake noise influencing air filter which does not substantially change the parts weight or the required installation space.
These and other objects of the invention are achieved by providing an air filter for an internal combustion engine, comprising an air filter housing having a housing wall which encloses a filter space, an unfiltered air inlet, and a filtered air outlet, wherein the housing wall includes at least one membrane portion that is more permeable to sound than the rest of the housing wall.
In accordance with a further aspect of the invention, the objects are achieved by providing a method of producing a sound transmitting filter housing comprising injection molding a filter housing of synthetic resin material with a housing wall and a membrane portion which has a greater permeability to sound than the rest of the housing wall.
The air filter according to the invention is advantageously suited to transmit sound such that the driver receives sufficient information on the operating state of the engine. The membrane, which is integrated in the housing wall and emits more sound than the housing wall itself, serves this purpose. By suitably arranging the membranes, e.g., directing them toward the engine, the intake noise can be reduced.
The membrane is connected with the housing wall to form a seal and thus represents a part of the boundary for a filter chamber. It must be installed on or in the housing wall in such a way that the air filter is sufficiently tight in every operating state. It must be kept in mind that the air filter is subjected to dynamic stresses in the form of air pressure changes, and that the membrane must not become detached from the housing wall and does not allow air leakage in any operating state. To this end, the membrane can be mounted on the housing wall from the outside or the inside. In either variant, a sufficient number of mounting points connecting the membrane to the housing wall must be provided.
The membrane is moreover configured in such a way that the air flowing through the filter, which comes from the inlet and flows through a filter element to the outlet, causes it to vibrate. These vibrations are transmitted to the surrounding components in the engine compartment and are finally directed into the passenger compartment or driver compartment. Depending on the requirements and the desired sound, several membranes of different shapes and sizes may be provided. Some possible shape variants involve the use of angular or oval membranes, which may have differently configured sound transmitting areas.
The membrane can be joined to the housing wall by gluing so as to form a seal. If the membrane is made of the same material as the filter housing, it can form an integral part of the filter housing. This avoids any possible leaks and saves assembly steps. A particularly suitable production method is the injection molding process.
One advantageous embodiment of the inventive concept involves the use of membranes with round or circular effective sound transmitting areas since they can be induced to vibrate particularly easily. Possible variants include embodiments in which angular membranes are inserted into the housing, but the effective sound transmitting areas themselves have round contours.
According to a further embodiment of the invention, the wall of the membrane can vary in its thickness. It is advantageous to make the areas of the edges of the membrane thin and the center area thick. As a result, the membrane can be quickly induced to vibrate but due to the thicker center area has sufficient mass to transmit the vibrations.
It is advantageous to give the membrane an undulating structure, which allows the membrane to vibrate more easily. A particularly advantageous solution is an embodiment where the membrane has an undulating structure along the periphery and a flat center area. In this case, the undulating area along the periphery can produce vibrations, which are then emitted by the flat center area. This embodiment provides the best results with respect to sound production and sound transmission.
In one specific embodiment, the membrane is arranged on an end face of the air filter housing. The end face is defined as the side, which the airflow meets after flowing through the air filter medium, so that the flow strikes the membrane directly and induces it to vibrate. This embodiment thus provides optimal sound transmission.
To install the membrane in the filter housing, it is advantageous to provide receiving or attachment areas in the filter housing. These receiving areas are used, for instance, to clip several mounting points of the membrane into the filter housing so that an adequate seal is provided, or to press the membrane into a circumferential groove on the filter housing, which receives the membrane and thus effects a sealing connection of the components. Other receiving areas can be configured in such a way that the melt of the membrane penetrates them and thereby effects an interlocking or form-fit connection between the membrane and the filter housing. In this case, the attachment area may take the form of conical bores with the cone opening toward the side opposite the membrane so that the membrane cannot fall out without being destroyed.
One method for producing the membrane and the filter housing is an injection molding process. The filter housing can be produced at a different location than the membrane. Moreover, a separate material can be selected for each component. The parts are subsequently joined.
A preferred variant is to make the membrane and the filter housing from the same material and in a single operation. In this case, the area of the membrane is distinguished from the filter housing wall only in its shape and its wall thickness. In this embodiment, no leaks will develop since there are no component boundaries between the membrane and the filter housing.
A further production variant is to injection mold the membrane into an existing filter housing. Here, the filter housing forms a part of the cavity for the membrane. This production method realizes an optimal fit of the membrane in the filter housing. Furthermore, the membrane can be injection molded in such a way that a permanent connection is created between the membrane and the filter housing.
A particularly advantageous production method is the two-component injection molding process. In this case, both components, the filter housing and the membrane, are produced in the same mold. After the filter housing has been injection molded first, slide gates recede and free the cavity for the membrane. With this production method, a finished component is obtained after unmolding.
These and other features of preferred embodiments of the invention, in addition to being set forth in the claims, are also disclosed in the specification and/or the drawings, and the individual features each may be implemented in embodiments of the invention either alone or in the form of subcombinations of two or more features and can be applied to other fields of use and may constitute advantageous, separately protectable constructions for which protection is also claimed.